Citizen divers help to count sharks

By Matthew Owens

Non-scientist divers are as good as acoustic telemetry in detecting and recording the profusion of shark populations, according to new research by Australian scientists. The team hopes that the divers will be able to aid in the monitoring and conservation of dwindling shark populations.

On the face of it, it doesn’t sound like the best idea to encourage Joe and Josephine public to scuba around the barrier reef counting sharks. But this is the conclusion from the latest research published today in the online academic journal PLOS ONE.

“Our study shows that with a little bit of training and a good sampling design, recreational divers collect very useful data that can be used to monitor shark populations over long periods of time and across large spatial areas.

Explains lead author Gabriel Vianna, from the University of Western Australia.

“Such programs have relatively small costs when compared with other methods currently used.”

Sharks, along with rays, skates and chimaeras, form a class of fish (Chondrichthyes) that has been around for about 400 million years. Now though, primarily due to our increasing demand for fish on the table, shark populations are waning. Similar to the situation with whales that eventually lead to a global moratorium on hunting in the 1980s, it is feared that the number of shark deaths is reaching an unsustainable level. Yet knowing the extent of the damage is half the problem – one that has proved to be tricky to overcome because the sharks are spread out thinly and need to be followed-up over many years.

For the study, Vianna and colleagues tested the accuracy of over 60 professional guide divers in their shark-spotting abilities after a total of more than 2,300 dives. Crucially, their results were checked against those from acoustic telemetry (a bit like gps on your phone- but using acoustic ‘pings’) – a gold standard measurement used as a comparison. The data were collected at coral reefs on the Pacific island of Palau over five years. The majority of sharks observed were the grey reef and the whitetip reef sharks.

The results showed a close association between the divers’ and telemetry scores (0.7 – where scores range from 0 to 1), suggesting that divers could be used to count the sharks with a good deal of accuracy. The study also used the telemetry to check whether the presence of the divers disturbed the sharks by altering their behaviour – which it did not. Therefore, it is suggested that using divers in this way is unlikely to adversely affect sharks in their natural habitat.

Although shark attacks are relatively rare (you are more likely to drown than be killed by a shark) a thought should be spared for any scuba divers out there in the ocean for extended periods. Both grey reef and whitetip reef sharks have been known to inflict mortal wounds on humans.